If you're going mechanical, why not pumped water storage instead? Nothing has to spin super fast and hydro has a lot of maturity.
(From a guy who got burned buying stock in a centrifugal system as my first "wicked smaht" investment as a 22yo).
(From a guy who got burned buying stock in a centrifugal system as my first "wicked smaht" investment as a 22yo).
Lifting an Olympic Swimming Pool (2.5 Mlitres) up 1 metre against gravity needs about 7kWh.
7kWh of Lithium battery is tiny, like three shoeboxes. And apparently costs about $1500 on eBay though I was expecting about $5k-$7k.
Surely it costs a lot more to buy two Olympic pools worth of land, dig it out, line it, and buy the turbines and pipes and stuff?
Dinorwig in Wales moves a lake 3.5km long and 26m deep, cost hundreds of millions to build, stores 9.1 GWh and Wikipedia says it’s questionable whether it’s financially viable in todays energy market, estimating 40 years to a return on investment for just arbitrage night to day electricity costs.
Surely that would store a lot of power, right? Lifting stuff is hard work, I thought. Showing my working so people can poke holes in it:
1000kg is a ton x 5 metres is two storey of a house x 9.8 Earths gravity constant = 49000 Joules is 13.6 Watt hours is …
… not going to power a house very long. it might mostly charge an iPhone 13 mini battery.
Lifting a Ford F-150 at 2.2 tons (5000 lbs) gets to 30 Watt Hours.
A household might use 10kWh in a day, or 660 tons lifted 5 meters to store that and round it up to roughly 1000 tons to give room for conversion losses to get that much electric power out of the system.
So 400+ Ford F-150s lifted up two storeys to store a house’s power for a day.
Convert that to water (1litre weighs 1kg and a cubic meter to a ton) and we are back in the realms of an Olympic swimming pool as a standard size, 40% of one going up 5m this time.
At home, the scaffolding required to take that weight and the space required to lift hundreds of cars or hundreds of tons of water would be immense. We’re talking a town water tower.
And of course you can trade less water going higher but then need more vertical space and if it’s on a hill, more sideways space for the gradient.
The other way I’m amazed is how energy dense LiIon batteries are, fossil fuels are way more dense, and human bodies are very efficient at 2000 Calories/day is about 2.2 Watt-hours.
Putting a ton of smaller chemical batteries at distribution substations means when the grid is at the peak, you can cover that peak without transmitting that power over the transmission system. Putting the battery near the consumer will take a big load off of the transmission system which as much of a bottleneck as the lack of generating facilities